Fluctuation of RPMs

[sermend75]

I replaced my BOSCH platinum 4 spark plugs on my VR6 12V a week ago and now every time I get to a stop sign, press the clutch and wait, I see my rpms fluctuate actively between 700 and 1000... I'm pretty much sure it didn't happen before... Any experiences? I replaced the BOSCH for OEM NGK's... do you think that could be the problem? Maybe the wires? I already ordered new wires just in case...

[masterqaz]

Did you unhook the battery when you changed the plugs?

[sermend75]

Now that you say it... no... I didn't do it... and actually, I had to replace the battery afterwards, it was basically... dead... would you expand on this? I really appreciate it... thanks...

[masterqaz]

If you unhooked the battery in anyway the throttle body will have lost its calibration. When this happens the ecu isnt sure exactly where the throttle plate is. Now some times it'll cause little issues and other times it may cause stalling issues.

It'll have a general idea of where it is but without the calibration/adaptation it wont know precisely.

On mk3 cars which are drive by cable its pretty simple. Key up but dont start, wait a few mins then key off. Wait a few more mins then start the car. You may have to do it several times. Ive had to do it up to 5 or 6 times on my vrt after unhooking the battery.

You can also do this with vag com.

It also helps to leave the car running at idle for a while, as unplugging the battery also zeros fuel trims.

[sermend75]

If you unhooked the battery in anyway the throttle body will have lost its calibration. When this happens the ecu isnt sure exactly where the throttle plate is. Now some times it'll cause little issues and other times it may cause stalling issues.

It'll have a general idea of where it is but without the calibration/adaptation it wont know precisely.

On mk3 cars which are drive by cable its pretty simple. Key up but dont start, wait a few mins then key off. Wait a few more mins then start the car. You may have to do it several times. Ive had to do it up to 5 or 6 times on my vrt after unhooking the battery.

You can also do this with vag com.

It also helps to leave the car running at idle for a while, as unplugging the battery also zeros fuel trims.

But I didn't unplug the battery... well... the day after, I had to replace the battery, so the car had no power for 2 days... but all the plugs and wires were already connected... do you think that might be the problem? I'll try to do what you say and see if it works... thanks...

[Kenji]

But I didn't unplug the battery... well... the day after, I had to replace the battery, so the car had no power for 2 days... but all the plugs and wires were already connected... do you think that might be the problem? I'll try to do what you say and see if it works... thanks...

You don't need VAG-COM. All you probably need to do is to reset your ECU as described in the last post in this thread.